Disclosed is an apparatus and method for diagnostically testing circuitry within a device. The apparatus and method incorporate the use of energy (e.g., light, heat, magnetic, electric, etc.) applied directly to any location on the device that can affect the electrical activity within the circuitry being tested in order to produce an indicator of a response. A local sensor (e.g., photonic, magnetic, etc.) is positioned at another location on the device where the sensor can detect the indicator of the response within the circuitry. A correlator is configured with response location correlation software and/or circuit tracing software so that when the indicator is detected, the correlator can determine the exact location of a response causing a device failure and/or trace the connectivity of the circuitry, based upon the location of the energy source and the location of the sensor.